x86: fix WARN_ON() message: teach page_is_ram() about the special 4Kb bios data page

This patch teaches page_is_ram() about the fact that the first
4Kb of memory are special on x86, even though the E820 table
normally doesn't exclude it.

This fixes the WARN_ON() reported by Laurent Riffard who was also
very helpful in diagnosing the issue.

[ mingo@elte.hu: we are working on doing this properly in the e820
  space, but for 2.6.25 this is the better fix. ]

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 9f42d7e9c158..7fb6eff644b3 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -42,6 +42,15 @@ int page_is_ram(unsigned long pagenr)
         unsigned long addr, end;
         int i;
 
+        /*
+         * A special case is the first 4Kb of memory;
+         * This is a BIOS owned area, not kernel ram, but generally
+         * not listed as such in the E820 table.
+         */
+        if (pagenr == 0)
+                return 0;
+
+
         for (i = 0; i < e820.nr_map; i++) {
                 /*
                  * Not usable memory: